JP2007184879A - Wireless lan device, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve suppression of frame collision between a wireless terminal whose signal intensity when receiving a frame is not higher than a fixed value, including a hidden terminal and a wireless base station or other wireless terminals, and to provide the improvement of the throughput of a data frame, under a wireless LAN environment comprising a plurality of wireless terminals and the wireless base station or a plurality of the wireless terminals. <P>SOLUTION: This wireless LAN device determines the presence/no presence of a low receiving signal intensity terminal when transmitting a frame (S11). When the low receiving signal intensity terminal is present, an RTS (Request to Send) and a CTS (Clear to Send) are transmitted (S21 and S22), and then, the frame is transmitted (S31). On the other hand, when no low receiving signal intensity terminal is present, the frame is immediately transmitted (S31). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wireless LAN device, and more particularly to a technique for improving throughput in a wireless LAN in which there is a terminal whose signal strength at the time of reception is a certain value or less.

  In recent years, wireless LAN has been widely used as one of means for connecting information devices such as personal computers and peripheral devices to a network. Since a wireless LAN system uses space as a medium for connecting to a network, it is easier to install and relocate compared to a wired LAN system that uses a twisted pair cable, coaxial cable, optical cable, or the like as the medium. There is an advantage that information devices and peripheral devices (hereinafter referred to as wireless terminals) can be used at any place within the reach of

  However, in the wireless LAN, there is a case where the existence of the other party is unknown because the radio waves do not reach each other directly because there is an obstacle between the wireless terminals. Such a wireless terminal is called a hidden terminal, but a standard in which a plurality of wireless LAN terminals senses a channel at the time of transmission, confirms that the channel is not used, and transmits the channel at the same time (for example, In IEEE802.11), since carrier sense does not function effectively for hidden terminals, it is not possible for hidden terminals called CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance). An access method with a collision avoidance function is used.

  The collision avoidance procedure for the hidden terminal in CSMA / CA includes RTS (Request to Send) and CTS (Clear to Send :) between the destination base station and the wireless terminal prior to data frame transmission. This is realized by exchanging a control frame called “ready for reception completion”, and other wireless terminals refraining from transmission for a period described in the duration field of the RTS and CTS frames. Here, a radio terminal that can receive RTS transmits with the value of the duration field of RTS, and a radio terminal that is a hidden terminal that cannot receive RTS transmits with the value of the duration field of CTS transmitted from the destination base station or radio terminal. Refrain. However, if the collision avoidance procedure is applied prior to transmission of all data frames, the throughput of the data frames will be lowered. For this reason, in order to suppress a decrease in the throughput of the data frame, in the conventional standard (for example, IEEE 802.11), a threshold for the length of the data frame to which the collision avoidance procedure is applied is set separately, and only for data frames longer than the threshold. The method of applying the collision avoidance procedure is taken.

Also, as disclosed in Patent Document 1 and Patent Document 2, there is a method for detecting a hidden terminal and suppressing a decrease in data frame throughput by applying a collision avoidance procedure prior to data frame transmission only when there is a hidden terminal. is there.
Japanese Patent No. 3155492 JP 2002-217913 A

However, attention has not been paid to a terminal that is not a hidden terminal but has a signal strength at the time of frame reception of a certain value or less. A relationship between terminals in which the signal strength at the time of frame reception is a certain value or less will be described with reference to FIG. 10 and FIG.
10 and 11, 51 and 61 are wireless terminals, 52 is a range in which a frame transmitted from the wireless terminal 51 can be received, and 53 is a frame that can be received from the wireless terminal 51 with a signal strength greater than a certain value. It is a range. Similarly, 62 is a range in which a frame transmitted from the wireless terminal 61 can be received, and 63 is a range in which a frame transmitted from the wireless terminal 61 can be received with a signal strength of a certain value or more. A range outside 53 and inside 52 is a range in which the signal intensity at the time of receiving a frame transmitted from the wireless terminal 51 is a certain value or less. Similarly, the range outside 63 and inside 62 is a range in which the signal intensity at the time of receiving a frame transmitted from the wireless terminal 61 is a certain value or less.

In FIG. 10, both the wireless terminals 51 and 61 are within the range where the signal strength at the time of receiving a frame transmitted from the other party is below a certain value. Career sense is susceptible to disturbances.
In FIG. 11, the signal strength at the time of receiving a frame from the wireless terminal 61 in the wireless terminal 51 is less than a certain value, but the wireless terminal 61 is outside the reception range of the frame from the wireless terminal 51. The wireless terminal 61 is a hidden terminal of the wireless terminal 51. However, since the wireless terminal 51 does not become a hidden terminal of the wireless terminal 61, the collision avoidance procedure is not properly executed only by the conventional hidden terminal countermeasure, so that the frame collision occurs. May occur, resulting in a low data frame throughput.

  The present invention has been made in consideration of the above-described situation, and in receiving a frame including a hidden terminal in a wireless LAN environment composed of a plurality of wireless terminals and a wireless base station or a plurality of wireless terminals. It is an object of the present invention to suppress the collision of frames between a wireless terminal whose signal strength is equal to or less than a certain value and a wireless base station or between wireless terminals, and to improve the data frame throughput.

In order to solve the above-mentioned problem, the invention according to claim 1 is a wireless LAN device that communicates wirelessly while sharing a predetermined band with another wireless terminal or a wireless base station, and a signal at the time of frame reception Low reception strength terminal determination means for determining presence / absence of a wireless terminal having a strength of a certain value or less, and frame transmission for controlling execution of a collision avoidance procedure between terminals at the time of frame transmission according to a determination result of the low reception strength terminal determination means And a control means.
The invention according to claim 2 is the wireless LAN device according to claim 1, wherein the frame transmission control means sets a threshold value of a length of a transmission frame to which a collision avoidance procedure between terminals is applied during frame transmission. The strength is changed depending on the presence or the number of wireless terminals having a certain strength or less.

Further, the invention of claim 3 is the wireless LAN apparatus according to claim 1 or 2, wherein the low reception strength terminal determination means is an average of signal strength when a frame transmitted from another wireless terminal is normally received. A value is calculated for each wireless terminal, and a wireless terminal whose signal strength at the time of frame reception is equal to or less than a certain value is determined based on the calculated average value.
According to a fourth aspect of the present invention, in the wireless LAN device according to the third aspect, the low reception strength terminal determination means determines the wireless terminal whose signal strength is a certain value or less for each wireless terminal whose reception is confirmed. This is performed every time a predetermined number of frames are received.

The invention according to claim 5 is the wireless LAN device according to claim 3, wherein the low reception strength terminal determination means performs determination of a wireless terminal having the signal strength equal to or less than a certain value at regular intervals. And
Further, the invention of claim 6 is the wireless LAN device according to claim 4 or 5, wherein the low reception strength terminal determination means determines the signal strength of the corresponding wireless terminal when the number of times of reception for a predetermined time is less than a predetermined value. The average value is not updated.

The invention according to claim 7 is the wireless LAN device according to claim 4 or 5, wherein the low reception strength terminal determination means is applicable when the number of receptions for a certain period of time continues to be 0 or less than a certain value. The wireless terminal is deleted from the determination target.
The invention according to claim 8 is the wireless LAN device according to claim 4, 5, 6 or 7, wherein the low reception strength terminal determination means is used for determination of a wireless terminal whose signal strength is a predetermined value or less. The reception signal strength data storing means for storing the original address and the average value of the signal strength when the frame from the transmission source address is received and the data used for calculating the average value are provided.

The invention according to claim 9 is the wireless LAN device according to any one of claims 1 to 8, wherein the low reception strength terminal determination means uses a transmission request frame for calculating the average value of the signal strength. It is characterized by doing.
The invention according to claim 10 is the wireless LAN device according to any one of claims 1 to 8, wherein the low reception strength terminal determination unit uses a reception ready frame for calculating the average value of the signal strength. It is characterized by using.

The invention according to claim 11 is the wireless LAN device according to any one of claims 1 to 8, wherein the low reception strength terminal determination means uses a probe response frame to calculate the average value of the signal strength. It is characterized by doing.
The invention of claim 12 is a program for causing a computer to function as the wireless LAN device according to any one of claims 1 to 11.
A thirteenth aspect of the present invention is a computer-readable recording medium on which the program according to the twelfth aspect is recorded.

  Advantageous Effects of Invention According to the present invention, it is possible to suppress the collision of frames between a wireless terminal whose signal strength at the time of receiving a frame including a hidden terminal and a wireless base station or between wireless terminals is less than a certain value, and to improve the throughput of the data frame. Can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an example of the configuration of a wireless LAN device according to the present invention. In the figure, 1 is a wireless LAN device, 2 is an antenna for wireless communication with a wireless LAN device 1 such as another STA (Station) or AP (Access Point), and 3 is a connection of the wireless LAN device 1. The main CPU of the device to be connected, 4 is the memory of the device to which the wireless LAN device 1 is connected, 5 is the main CPU 3 of the device to which the wireless LAN device is connected, the wireless LAN device 1, the memory 4 and other communication interfaces, etc. Is a bus that connects In the present embodiment, the wireless LAN device 1 is connected to and operated by another device such as a personal computer. However, the wireless LAN device 1 is not limited to a personal computer, but is a part of a wireless terminal such as an STA or an AP or a wireless base station. You may connect so that it may operate.

  The wireless LAN device 1 further includes a baseband unit 10 and an RF unit 9. In the baseband unit 10, 11 is a local CPU, 12 is a MAC (Medium Access Control), 13 is a PLCP (Physical Layer Convergence Protocol), 14 is an AD / DA conversion circuit, and 16 is a firmware for operating the local CPU 11. Reference numeral 17 denotes a work RAM of the local CPU 11, and 18 denotes an interface circuit with a device to which the wireless LAN device 1 is connected. Reference numeral 15 in the RF unit 9 denotes an RF (Radio Frequency) circuit.

The operation of each module in the wireless LAN device 1 is as follows.
First, a procedure for transmitting data from a device (hereinafter referred to as a user circuit) to which the wireless LAN device 1 is connected and a frame for wireless LAN management (management) from the wireless LAN device 1 will be described. Data of the user circuit is output from the memory 4 on the bus 5 or another module (not shown) to the MAC 12 via the interface circuit 18 by the main CPU 3. A frame for wireless LAN management is created on the work RAM 17 by the local CPU 11 and output to the MAC 12.

The MAC 12 adds data for controlling the PLCP 13 and management data (header) determined by the wireless LAN standard to the input user circuit data and wireless LAN management frame. Then, data encryption processing and fragment processing (data subdivision) are performed, converted into a frame conforming to the wireless LAN standard, and output to the PLCP 13.
The PLCP 13 modulates the frame based on the data for controlling the PLCP 13 on the header of the frame input from the MAC 12 according to a method determined for each transmission speed by the wireless LAN standard, and outputs it to the AD / DA conversion circuit 14. To do. The AD / DA conversion circuit 14 converts the modulated digital signal frame input from the PLCP 13 into an analog signal and outputs the analog signal to the RF circuit 15. The RF circuit 15 performs processing such as amplification and frequency conversion on the frame converted into the analog signal by the AD / DA conversion circuit 14 and transmits the processed signal from the antenna 2.

Next, a procedure for outputting the data frame received by the wireless LAN device to the user circuit and outputting the management frame to the work RAM 17 of the local CPU 11 will be described.
Analog signals of data frames and management frames transmitted from other STAs and APs such as STAs and APs input from the antenna 2 are subjected to processing such as amplification and frequency conversion by the RF circuit 15 and output to the AD / DA conversion circuit 14 Is done.
The AD / DA conversion circuit 14 converts the analog signal input from the RF circuit 15 into a digital signal and outputs the digital signal to the PLCP 13. The PLCP 13 demodulates the signal from the AD / DA conversion circuit 14 by a method determined for each transmission speed by the wireless LAN standard and outputs the demodulated signal to the MAC 12.

In the MAC 12, the data frame and management frame input from the PLCP 13 are decrypted when the frame is encrypted based on the management data (header), and defragmented when the frame is fragmented ( The data frame is finally output as data to the memory 4 on the bus 5 or another module (not shown) via the interface circuit 18, and the management frame is the work RAM 17 of the local CPU 11. Is output.
In addition to the processing related to the data frame and management frame described above, the MAC 12 generates a control frame for performing control of the wireless LAN, performs transmission / reception processing, time management related to the timing of data transmission based on the received control frame, etc. Processing is also performed. Furthermore, a detection process of a low reception strength terminal, which will be described later, and a collision avoidance measure during frame transmission based on the result are performed. As for the operation at the time of transmission / reception of the control frame, the MAC 12, the PLCP 13, the AD / DA conversion circuit 14, and the RF circuit 15 perform the same operation as the transmission / reception operation of the data frame and the management frame.

  Further, the local CPU 11 is connected to the main CPU 3 of the user circuit via the interface circuit 18 and the bus 5, and further connected to the MAC 12, the RF circuit 15, the memory 16 with firmware and the work RAM 17 through a dedicated or common bus, The operation of each module is controlled based on a command from the main CPU 3 or firmware loaded in the memory 16. In particular, the MAC 12 may be subjected to many processes such as setting, interrupt processing, error processing, fragment processing, and defragment processing. In the present invention, the local CPU 11 detects a wireless terminal whose signal intensity at the time of frame reception is a predetermined value or less based on a program (firmware) in the memory 16, and performs control for avoiding collision at the time of frame transmission. The work RAM 17 is used for the purpose of temporarily storing data when the local CPU 11 performs processing on the MAC 12.

Next, a method for detecting a wireless terminal whose signal strength at the time of frame reception in the MAC 12 of the wireless LAN device 1 of FIG. 1 is a certain value or less will be described with reference to FIGS.
FIG. 2 is a flowchart illustrating an example of a process for updating the received signal strength table. When a frame is input from the PLCP 13 to the MAC 12, the frame type and subtype are extracted from the frame control field of the MAC header (step 101), and it is determined whether the frame is of a type used for detection (step 102). If the frame is not to be detected, normal reception processing is performed (step 120). The detection target frames include the RTS, CTS, and Probe Response frames described above.
In the case of the frame of the corresponding type in step 102, the source address is extracted from the MAC header (step 111), and the received signal strength table is searched for whether it is the source address of the terminal that has already been received (step 112). ), It is determined whether or not the source address is existing (step 113). The received signal strength table referred to here is a transmission source address, an average value of signal strength when a frame is received from the transmission source address, and data used to calculate an average value for each transmission source address. Alternatively, it is held in a storage circuit such as a register (see FIG. 3).

If the source address is present in the received signal strength table in step 113, the received signal strength calculation process for that address is performed (step 115), and the normal reception process is performed (step 120).
On the other hand, if the source address does not exist in the received signal strength table in step 113, the source address is added to the received signal strength table (step 114). Next, received signal strength calculation processing for the address is performed (step 115), and normal reception processing is performed (step 120).
The structure of the RTS frame and Probe Response frame used for detection of the low reception strength terminal in the present invention, the frame control field in the MAC header, the frame type, subtype, and transmission source address are as shown in FIG. It is.
In this example, a normal reception process (step 120) is performed after a series of processes from the source address extraction (step 111) surrounded by a dotted line to the received signal strength calculation process (step 115). May be performed in parallel.

  FIG. 4 is a flowchart showing an example of the received signal strength calculation process (step 115) of FIG. In this procedure, since a flag (init) indicating whether or not to perform initialization and a source address (SA) are passed from the caller as an argument, first, init is 1 as to whether the source address is newly added. (Step 151). If new (step 151 is Y), in step 114 of FIG. 2, the received signal strength integrated value pwr_int (SA) and the average received signal strength pwr_avg (SA) are detected in the received signal strength table simultaneously with the new source address. Since the reception count count (SA) of the type of frame to be used has been added, each is initialized by substituting 0 (step 152). If it is not new (if step 151 is N), this initialization step is not performed.

Next, a value obtained by adding the received signal strength pwr_now of the frame from the RF circuit 15 of FIG. 1 to pwr_int (SA) is substituted into pwr_int (SA), and 1 is added to count (SA) (step 153). Then, it is determined whether or not count (SA) has reached the prescribed number of times n (> 0) (step 154). If count (SA) has not reached n, the process ends and returns to the caller.
On the other hand, when count (SA) reaches the prescribed number n (> 0) in step 154, a value obtained by dividing pwr_int (SA) by n is substituted for pwr_avg (SA) (step 155), and pwr_int (SA) and Substitute 0 in each of count (SA) (step 156) and return to the caller. The number of times n depends on the number of wireless terminals that communicate simultaneously, particularly the number of wireless terminals that move, but may be about 50 to 100 times. The error increases at the time of determination whether it is too much or too little.

  FIG. 5 is a flowchart showing another example of the received signal strength calculation process (step 115) of FIG. First, it is determined whether the init is 1 or not (step 161). In the case of new (step 161 is Y), in step 114 of FIG. 2, the received signal strength integrated value pwr_int (SA) and average received signal strength pwr_avg (SA) are detected in the received signal strength table simultaneously with the new source address. Since the reception count count (SA) and reference reception time time (SA) of the type of frame to be used are added, initialization is performed by substituting 0 for each except for time (SA). The time (SA) is initialized by reading and substituting the current time t from a calendar clock (not shown) (step 162). If it is not new (if step 161 is N), this initialization step is not performed.

Next, a value obtained by adding the received signal strength pwr_now of the frame from the RF circuit 15 of FIG. 1 to pwr_int (SA) is substituted into pwr_int (SA), and 1 is added to count (SA) (step 163).
Then, it is determined whether or not t (current time) -time (SA) has reached a specified time t1 (> 0) (step 164). If the specified time t1 (> 0) has not been reached, the process is terminated and the process returns to the caller.
On the other hand, if t-time (SA) has reached the specified time t1 (> 0) in step 164, the reception count count (SA) of the type of frame that uses pwr_int (SA) for detection in pwr_avg (SA). The divided value is substituted (step 165), 0 is substituted for pwr_int (SA) and count (SA), and t is substituted for time (SA) (step 166), and the process returns to the caller. Note that the specified time t1 may be several tens of seconds to several minutes, although it depends on the number of wireless terminals that communicate simultaneously, particularly the number of wireless terminals that move, as with the above-described frame reception count n. The same applies to the case where the number of frame receptions is n. However, if the average value is frequently updated, the number of terminals that do not reach the number of frame receptions n increases and the accuracy of the average value decreases, and the load on the local CPU 11 increases. Reduce efficiency.

As described above, when there is a terminal whose average received signal strength pwr_avg (SA) for each transmission source terminal (= SA) obtained in FIG. 4 or FIG. 5 is a certain value or less, it is determined that there is a low received signal strength terminal. . In FIG. 5, time (SA) records the reference reception time separately for each transmission source terminal (SA), but the same value may be used for all transmission source terminals. Although not shown in the flowchart in this case, the transmission source terminal newly added to the received signal strength table is not necessarily subjected to the received signal strength calculation process after t1. Therefore, pwr_int (SA) and count (SA) may not be reflected in pwr_avg (SA).
For the same reason, when the number of receptions count (SA) for a certain time is equal to or less than a certain value, the average value pwr_avg (SA) of the signal strength of the corresponding source address is not updated. Further, when the number of receptions count (SA) for a certain time is 0 or a state where the number of receptions is less than or equal to a certain value continues for a plurality of times, the corresponding transmission source address SA, its average received signal strength pwr_avg (SA), The pwr_int (SA), the reception count count (SA) of the type of frame used for detection, and the like are deleted from the received signal strength table.

  In the above-described processing, whether the specified time t1 has been reached is obtained based on the time read from the calendar clock, but the time does not have to be a unit of hour / minute / second used in daily life. A timer that increments at a predetermined time interval (for example, 1 second) may be used to hold time in seconds in time (SA), or the elapsed time itself may be held. In the case of the elapsed time, it is initialized to 0 at the time of initialization, and the time elapsed from the initialization is held in time (SA).

6 to 8 are flowcharts showing a procedure at the time of frame transmission. The procedure will be described below. Note that, for the sake of simplicity of explanation, the description when the RTS transmission and the frame transmission are retransmitted is omitted.
FIG. 6 determines whether to perform RTS / CTS before frame transmission according to the presence / absence of a low reception signal strength terminal, and determines the presence / absence of a low reception signal strength terminal at the time of frame transmission (step 11). Here, when there is a terminal with low received signal strength, RTS and CTS are transmitted (steps 21 and 22), and then a frame is transmitted (step 31). On the other hand, if there is no terminal with low received signal strength, the frame is immediately transmitted (step 31). The presence / absence of a low reception signal strength terminal is determined based on the reception signal strength table described above based on whether there is a terminal having an average reception signal strength pwr_avg (SA) of a predetermined value or less.

Next, FIG. 7 changes the frame length (threshold value) when transmitting an RTS depending on the presence / absence of a low reception signal strength terminal. The presence / absence of a low reception signal strength terminal is determined during frame transmission (step 11). If there is no received signal strength terminal, the frame length at the time of RTS transmission is set to m (step 12), and if there is a low received signal strength terminal, the frame length is set to n (step 13). Here, the relationship between m and n is 0 ≦ n <m.
Next, it is determined whether or not RTS / CTS transmission is performed based on whether or not the length of the transmission frame is longer than the RTS frame length set previously (step 14).
If the length of the transmission frame is larger than the RTS frame, RTS and CTS are transmitted (steps 21 and 22), and then the frame is transmitted (step 31).
On the other hand, if the length of the transmission frame is equal to or shorter than the RTS frame length, the frame is immediately transmitted (step 31).

In FIG. 8, the RTS frame length (threshold value) is changed by the number of low received signal strength terminals. The number of low received signal strength terminals is determined at the time of frame transmission (step 15). The frame length is set to a (step 16), if X <number of terminals <Y, the RTS frame length is set to b (step 17), and if the number of terminals ≧ Y, the RTS frame length is set to c (step 16). Step 18). Here, the relationship between X and Y is 0 ≦ X <Y, and the relationship between a, b, and c is 0 ≦ c <b <a.
Next, it is determined whether or not to perform RTS / CTS transmission based on whether or not the length of the transmission frame is longer than the RTS frame length (step 14). If the length of the transmission frame is larger than the RTS frame length, RTS and CTS are transmitted (steps 21 and 22), and then the frame is transmitted (step 31). On the other hand, if the length of the transmission frame is equal to or shorter than the RTS frame trillion, the frame is immediately transmitted (step 31).

  In FIG. 8, the number of branches in step 15 is not necessarily three, and it is sufficient if there are two or more branches. The values of m and n in FIG. 7, a and b and c in FIG. 8, and the values of X and Y are fixed in the figure, but can be changed as necessary as long as the respective magnitude relationships are maintained. Also good. Furthermore, although the above description has been made with IEEE 802.11 as an example, the present invention is not limited to IEEE 802.11, and can be applied to similar wireless LANs.

It is a figure which shows the example of a structure of the wireless LAN apparatus concerning this invention. It is a flowchart which shows the example of the update process of a received signal strength table. It is a figure which shows an example of a received signal strength table. It is a flowchart which shows an example of a received signal strength calculation process. It is a flowchart which shows the other example of a received signal strength calculation process. It is a flowchart which shows the procedure at the time of frame transmission. It is a flowchart which shows the procedure at the time of frame transmission. It is a flowchart which shows the procedure at the time of frame transmission. It is a figure which shows the structure of a RTS frame and a Probe Response frame. It is a figure explaining the relationship between the terminals from which the signal strength at the time of frame reception becomes below a fixed value. It is a figure explaining the relationship between the terminals which become a hidden terminal at the time of frame reception.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Wireless LAN apparatus, 2 ... Antenna, 3 ... Main CPU, 4 ... Memory, 5 ... Bus, 9 ... RF part, 10 ... Baseband part, 11 ... Local CPU, 12 ... MAC, 13 ... PLCP, 14 ... AD / DA conversion circuit, 15 ... RF circuit, 16 ... firmware memory, 17 ... work RAM, 18 ... interface circuit

Claims (13)

  A low-reception-strength terminal determination for determining whether or not there is a wireless terminal whose signal strength at the time of frame reception is a certain value or less, which is a wireless LAN device that communicates wirelessly while sharing a predetermined band with other wireless terminals or wireless base stations And a frame transmission control means for controlling execution of a collision avoidance procedure between terminals at the time of frame transmission according to a determination result of the low reception strength terminal determination means.   The frame transmission control means is configured to change a transmission frame length threshold to which a collision avoidance procedure between terminals is applied during frame transmission depending on the presence or the number of wireless terminals having a signal strength equal to or less than a predetermined value. The wireless LAN device according to claim 1.   The low reception strength terminal determination means calculates an average value of signal strength when a frame transmitted from another wireless terminal is normally received for each wireless terminal, and the signal strength at the time of frame reception is calculated based on the calculated average value. 3. The wireless LAN device according to claim 1, wherein a wireless terminal having a predetermined value or less is determined.   4. The low reception strength terminal determination unit performs determination of a wireless terminal having the signal strength of a predetermined value or less every time a predetermined number of frames are received for each wireless terminal confirmed to be received. Wireless LAN device.   4. The wireless LAN device according to claim 3, wherein the low reception strength terminal determination unit performs determination of a wireless terminal having the signal strength of a predetermined value or less at regular intervals.   6. The wireless LAN according to claim 4, wherein the low reception strength terminal determination unit does not update the average value of the signal strength of the corresponding wireless terminal when the number of receptions for a predetermined time is equal to or less than a predetermined value. apparatus.   The said low receiving strength terminal determination means deletes a corresponding wireless terminal from the determination target when the number of times of reception for a certain period of time is zero or a state below a certain value continues. Wireless LAN device.   The low reception strength terminal determination means calculates a transmission source address used for determination of a wireless terminal having a signal strength of a certain value or less, and an average value and an average value of signal strength when a frame is received from the transmission source address. 8. The wireless LAN device according to claim 4, further comprising reception signal strength data storage means for storing data to be used for the purpose.   9. The wireless LAN device according to claim 1, wherein the low reception strength terminal determination unit uses a transmission request frame for calculating the average value of the signal strength.   The wireless LAN device according to any one of claims 1 to 8, wherein the low reception strength terminal determination unit uses a reception preparation completion frame for calculating the average value of the signal strength.   The wireless LAN device according to any one of claims 1 to 8, wherein the low reception strength terminal determination unit uses a probe response frame to calculate the average value of the signal strength.   The program for functioning a computer as a wireless LAN apparatus of any one of Claims 1 thru | or 11.   A computer-readable recording medium on which the program according to claim 12 is recorded.

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